On Friday, a group of hackers targeted computer infrastructure in Russia and Iran, impacting internet service providers, data centres, and in turn some websites. In addition to disabling the equipment, the hackers left a note on affected machines, according to screenshots and photographs shared on social media: “Don’t mess with our elections,” along with an image of an American flag.

Now, the hackers behind the attack have said why they did it.

“We were tired of attacks from government-backed hackers on the United States and other countries,” someone in control of an email address left in the note told Motherboard Saturday.

In a blog post Friday, cybersecurity firm Kaspersky said the attack was exploiting a vulnerability in a piece of software called Cisco Smart Install Client. Using computer search engine Shodan, Talos (which is part of Cisco) said in its own blog post on Thursday it found 168,000 systems potentially exposed by the software. Talos also wrote it observed hackers exploiting the vulnerability to target critical infrastructure, and that some of the attacks are believed to be from nation-state actors. Indeed, Talos linked the recent activity to a March alert from the US Computer Emergency Readiness Team (CERT), which said Russian government hackers were targeting energy and other critical infrastructure sectors.

Presumably, this is what this week’s vigilante hackers were responding to.

“We simply wanted to send a message,” they told Motherboard.

A screenshot of the message the hackers left on impacted machines. Image: Twitter

The attack itself seems to be relatively unsophisticated. Lower-skilled hackers have previously created tools that can serve a similar, scattershot purpose. In January, a pseudonymous security researcher released AutoSploit, a tool that scanned computer search engine Shodan for vulnerable machines and then fired exploits from the penetration testing tool Metasploit. This new attack appears to be similar somewhat in approach.

Regardless, this attack has had an impact. In its blog post Kaspersky said the attack had targeted the Russian speaking segment of the internet. And in a statement carried by Iran’s official news agency IRNA, the Communication and Information Technology Ministry said “The attack apparently affected 200,000 router switches across the world in a widespread attack, including 3,500 switches in our country.” Reuters reported that Iran’s IT Minister Mohammad Javad Azari-Jahromi said the attack mainly impacted Europe, India, and the US. In a tweet he added that 95 percent of the routers have resumed normal functioning.

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The hackers said they did scan many countries for the vulnerable systems, including the UK, US, and Canada, but only “attacked” Russia and Iran, perhaps referring to the post of an American flag and their message. They claimed to have fixed the Cisco issue on exposed devices in the US and UK “to prevent further attacks.” In its blog post, Talos suggested system administrators could run a particular command on the affected device to mitigate the exposure. This is what the hackers claimed they did on machines in the UK and US.

“As a result of our efforts, there are almost no vulnerable devices left in many major countries,” they claimed in an email.

However, at the time of writing the number of exposed devices has only decreased marginally, from 168,000 at the time of Talos’ scan, to just over 166,000 on Saturday, according to search results on Shodan. 46,500 of those results are in the US. Motherboard will update this piece if more evidence becomes available for the hackers’ alleged patching.

Update: This piece has been updated to include more information from the Twitter account of Iran’s IT Minister Mohammad Javad Azari-Jahromi.